1. Field of the Invention
This invention relates to a search and rescue radar transponder (hereinafter referred to as "SART" in short) to receive transmitted signals from rescue radars (hereinafter referred to as "radars" in short) and to transmit rescue signals for informing the radars of its location.
2. Description of the Prior Art
FIG. 1 is a block diagram showing a structure of a prior art SART. In FIG. 1, reference numeral 1a designates an antenna for receiving radar signals (hereinafter referred to as "receiving antenna"); numeral 1b designates an antenna for transmitting rescue signals (hereinafter referred to as "transmitting antenna"); numeral 2 designates a receiving circuit to amplify and detect the radar signals received by the receiving antenna 1a; numeral 3 designates a transmitting circuit to generate rescue signals and output them to the transmitting antenna 1b; numeral 4 designates a controlling circuit to control the operation of the transmitting circuit 3 and the receiving circuit 2; numeral 5 designates an operating switch for operating this SART; and numeral 6 designates a power source to supply electric power to the receiving circuit 2, the transmitting circuit 3 and the controlling circuit 4.
FIG. 2 is a block diagram showing a structure of another prior art SART having an antenna for transmitting and receiving, which is commonly used as the transmitting antenna 1b and the receiving antenna 1a of FIG. 1. In FIG. 2, reference numeral 1 designates that antenna; and numeral 7 designates a changeover switch to change over the connection of the transmitting circuit 3 and the receiving circuit 2 to the antenna 1.
Next, the operation of the prior art SART will be described. SARTs operate in order to display their own locations on radar faceplates by receiving transmitted signals from the radars and transmitting specified rescue electric waves within receivable periods of the radars at the time of disasters. For this reason, the SARTs are begun to be used in large quantities as effective equipment, being all-weather and 24 hour type lifesaving appliances which are not influenced by the weather and time zones, for saving lives precisely and quickly.
Since the SARTs shown in FIG. 1 and FIG. 2 differ only in the point of using the antenna 1 in common or not, the description of their operation on the basis of the timing chart of FIG. 3 will be done only about that of the SART shown in FIG. 2, and the description of the operation of the SART shown in FIG. 1 will be omitted.
Although the SART is in its nonoperating state usually, electric power is supplied to the receiving circuit 2, the transmitting circuit 3 and the controlling circuit 4 from the power source 6 when a sufferer turns the operating switch 5 on at the time of his or her disaster. The controlling circuit 4 brings the receiving circuit 2 on its operating state (FIG. 3C) at first, and it changes over the changeover switch 7 to the contact "a" of the side of the receiving circuit 2 at the same time. In this state, if transmission signals from a radar are sent (FIG. 3A), these electric waves are received by the antenna 1 of the SART after some time delays in proportion to the distance between the radar and the SART (FIG. 3B). The transmission signals received by the antenna 1 are amplified and detected at the receiving circuit 2, then they are inputted to the controlling circuit 4. In the case where the signal levels of the inputted signals from the receiving circuit 2 are at a prescribed level or more, the controlling circuit 4 changes over the changeover switch 7 to the contact "b" of the side of the transmitting circuit 3 for generating rescue signals, and it outputs transmission-beginning signals to the transmitting circuit 3 at the same time (FIG. 3E). Then the controlling circuit 4 causes the transmitting circuit 3 to generate rescue signals to be sent to the air from the antenna 1 (FIG. 3D) so as to be received by radars.
Besides, the controlling circuit 4 controls the operation timing to stop the operation of the transmitting circuit 3 during the time of receiving operation of the SART and to stop the operation of the receiving circuit 2 during the time of transmitting operation of the SART in order to prevent misoperation by interference in transmitting and receiving operation of the SART (FIG. 3C), FIG. 3E).
Moreover, there are Published Unexamined Patent Applications to Japan No. 152886 of 1979 and No. 186184 of 1992 as documents describing preceding techniques related to the above mentioned prior art.
Since the prior art SARTs are constructed as mentioned above, the SARTs are left as they are in their nonoperating states for many hours normally, as the chance of meeting a disaster is rare in spite of being made so as to operate at the time of the disaster. Consequently, it is resulted whether the SARTs operate well or not at the time of a disaster is entrusted to the reliability of the SARTs proper and their preserved conditions. Moreover, the power sources used in the SARTs are generally primary batteries, so their terms of preservation are limited and the spans of their lives vary according to their preserved states. For that reason, it is necessary to check the operation of the SARTs periodically, but to check the SARTs proper by removing them from their installed places (such as vessels, lifeboats and the like) has such problems that it is elaborate and the inspecting apparatus for it also are large-scale and expensive.